Luckily I updated my ESXi about three days ago from 5.5 U2 to U3... However, I was lucky and the bug didn't occured yet on my environment, because the VMs are also saved in the root-folder of the datastore like tinto1970 does it too.
There is a new interesting post in the VMware community thread:
VMware Support-Team wrote:Last night engineering found the root cause. They will need to produce an express patch.
We have asked how long are we expecting to wait for this, I will follow up once a response has been received.